1. Field of Invention
The present invention relates to improved image display apparatus of the active type and more particularly to such apparatus having a unique capability for selectively reversing the reproduction sense of a displayed image.
2. Description of Prior Art
Present day information storage and retrieval systems include media for storing information in both positive and negative format, i.e., "positive format" being generally utilized in reference to the same image-sense as the original (dark portions of the original are dark and light portions light in the storage media) and negative format being generally utilized in reference to the reverse image sense as the original (dark portions of the original are light and light portions dark in the storage medium).
Display terminals for such information systems generally produce images for viewing which are the same reproduction (or image) sense as on the storage medium. The prior approaches for providing image-sense reversal at a display terminal have been by and large impractical, unreliable and/or extremely expensive and thus have not received any great extent of commercial success.
However, the need for an image reversal capability for such display terminals continues to exist for a number of reasons. For example certain stored information on the storage medium may be more readily discerned by the viewer in one image sense, while other information on the medium is more readily discerned in the other image sense. Also the desired reproduction sense for hard copy output from the system may be opposite that which is most desirable to view. Additionally a subjective factor exists, in that some viewers simply "prefer" one reproduction sense display while others "prefer" the other sense; thus the flexibility to vary this aspect at will is attractive for such apparatus.